Process for dissolution development using thiourea compounds as dmax maintainers



United States Patent O 3,495,982 PROCESS FOR DISSOLUTION DEVELOPMENT USING THIOUREA COMPOUNDS AS D, MAINTAINERS Ralph Kingsley Blake, Westfield, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed June 23, 1967, Ser. No. 648,250 Int. Cl. G03c 5/26, 1/02, 5/30 U.S. CI. 96-64 9 Claims ABSTRACT OF THE DISCLOSURE Process for forming a silver halide image by selectively exposing a photosoluble silver halide layer and dissolving the exposed photosoluble silver halide in a silver halide solvent, characterized by the solvent containing a D maintaining amount of a substituted thiourea compound devoid of ionizable iodine, or oxidizing or reducing groups which are active at the Working pH.

BACKGROUND OF THE INVENTION Cross-reference to related applications In assignees Ralph Kingsley Blake application entitled Photosolubilization Image Formation, and Jack Freshwater Strange application entitled Photosolubilization Process Using Phenols as D Maintainers executed and filed on even date with this application, there are described and claimed similar processes discolsing various D maintainers that are difierent from the thiourea compounds used in accordance with this invention.

Field of the invention This invention relates to a process for forming images from photosoluble (photosolubilizable) silver halide layers. The present invention constitutes an improvement in a silver halide photosolubilization process by the use of a substituted thiourea compound adjuvant which helps to prevent dissolution of silver halide in unexposed areas while allowing dissolution to proceed in the exposed areas. Because of this characteristic, the adjuvant can be characterized as a maximum density maintaining agent, or a D maintainer.

Description of the prior art Photosolubilization image-forming processes and photosoluble layers and elements useful in the process of the present invention are described in U.S. Patents 3,155,507 and 3,155,514 to 3,155,519 inclusive, patented Nov. 3, 1964; and in assignees applications U.S. Ser. No. 390,460 filed Aug. 8, 1964 (Blake U.S. Patent 3,384,485, May 21, 1968 and U.S. Ser. No. 629,462 filed Apr. 10, 1967; Blake and Fan U.S. Ser. No. 403,660 filed Oct. 13, 1964 (U.S. Patent 3,368,809, Feb. 13, 1968); Fan U.S. Ser. Nos. 403,631 and 403,632 filed Oct. 13, 1964 (U.S. Patents 3,407,067 and 3,407,068, Oct. 12, 1968); Hunt U.S. Ser. No. 388,919 filed Aug. 11, 1964; and Haugh U.S. Ser. No. 478,421 filed Aug. 9, 1965. In these patents and applications there are described simple and useful layers and processes for obtaining a positive silver halide image in a single processing step. Intensification of the 3,495,982 Patented Feb. 17, 1970 SUMMARY OF THE INVENTION This invention pertains to an improved photosolubilization process for forming a direct positive silver halide image Which comprises (a) Exposing, imagewise, a photosoluble layer containing silver halide made relatively less soluble in a silver halide solvent by treatment with an organic compound containing sulfur and/or nitrogen and capable of forming a silver salt of lower solubility in water than silver chloride; and

(b) Dissolving the exposed silver halide in a silver halide solvent comprising an aqueous bath of an alkali metal or ammonium thiosulfate, the improvement being characterized by the presence while said layer is in said bath at pH from 3 to 11, preferably 5 to 11, of D maintaining amounts of a substituted thiourea compound free from ionizable iodine, oxidizing groups or reducing groups which are active at the working pH, in sufiicient quantity to retard solution of the unexposed silver halide. A practical range is about 0.01 to about 2 g./liter. The upper limit is preferably less than 2 g./liter where that figure exceeds the solubility of the compound, although the undissolved excess will not be harmful.

In the layer of step (a), the organic compound is present in such an amount, in terms of the ratio of its weight to the surface area of the silver halide crystals, that when admixed in suchratio with an aqueous silver bromochloride (30/70 mole percent) gelatin dispersion containing 0.29 mg. of Ag in one-half ml., and said silver bromochloride dispersion is treated with 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag and mg. of sodium thiosulfate, at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively treated with 5% by weight aqueous sodium hypochlorite and 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag, 25 mg. of sodium hypochlorite and 100 mg. of sodium thiosulfate, after vigorous agitation of both dispersions for 30 seconds at 25 C.

The substituted thiourea compound should be devoid of ionizable iodine because the iodide ion readily replaces the organic compound of step (a) to form silver iodide; it should be devoid of oxidizing groups because these tend to oxidize the silver salts of the organic compound of step (a) so that exposed and unexposed areas cannot be easily distinguished in terms of their rates of solution in a silver halide solvent.

The substituted thiourea compound has from 1 to 4 of the hydrogen atoms of thiourea replaced with a larger group, preferably with a hydrocarbon group. This hydrocarbon group may be straight chain or branched chain, saturated or unsaturated aliphatic hydrocarbon group, aromatic or alicyclic hydrocarbon group. The minimum molecular Weight of useful compounds is 90.

The D -maintaining, substituted thiourea compound effects an improvement of the image by retarding the dissolution of silver halide preferentially in the unexposed as compared to the exposed areas of the photosoluble element. The presence of the D -maintaining compound has the advantage that less precise control of processing conditions may be tolerated, e.g., concentration of silver halide solvent, pH, and period of. time required to dis solve the exposed photosoluble silver halide image.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In practicing the process of ,the invention, a photosoluble silver halide layer as idefined in Blake U.S. 3,155,519, preferably a layer of silver chloride emulsion insolubilized with 2 mercapto-4-phenylthiazole or a related mercapt an as disclosed in said patent is prepared.

The element may advantageously have a photographic optical sensitizing dye associated with its silver halide crystals as disclosed in Blake, U.S. P. 3,384,485. The photosoluble layer is exposed, imagewise, to actinic radiation and then treated in an aqueous bath comprising from 0.1 to 2 moles per liter of a thiosulfate, e.g., sodium thiosulfate, silver l halide solvent and a substituted thiourea Dmax maintainer as defined above. A preferred such thiourea Dmax maintainer is 1-(1-naphthy1)-2- thiourea in a concentration of 0.01 to 2.0 g./liter, preferably from 0.05 to 0.3 g./liter. The time and ,temperature of treatment in the aqueous bath are obviously dependent variables but at a temperature of 70 F. the time should be about 1 to 5 minutes. This treatment removes silver halide from the exposed areas at a much faster rate than from the unexposed areas, leaving a positive silver halide image. The presence oLan organic compound such as 1-(l-naphthyDZ-thiourea further lowers the rate of dissolution of the unexposed silver. halide, relative to that of the exposed silver halide, contributing to better image formation, especially to higher densities in unexposed areas. A useful positive image can be produced, particularly; for viewing by projection, by this single treatment, although a washing step is generally used. For most purposes, it is desirable to intensify the silver halide image, usually by treating with a photographic silver halide developer solution to reduce. the image to one of black metallic silver. The silver halide image may be fogged prior to reduction by flashing to white light or, more conveniently, by use of a prefogged element such as desgribed in assignees copending applications, of Blake, U.S. Ser. No. 629,462, filed,Apr. 10,4967, and of Haugh U.S. Ser.,No. 478,421, filed Aug. 9, 1965. Other methods of intensifying the silver halide image, eg, by toning, color developing, etc., are disclosed in U.S. 3,155,507.

Any of the various photosoluble silver halide elements idescribed in the U.S. patents and Blake and Haugh applications listed above canbe used in the Process of his invention. These, of course, may be modified as described in the patents and applications by variations in the silver halide,; the binder (if present), the organic compounds for insolubilization of silver halide (whose utility can be established by the simple tests defined therein for determination of other useful compounds), the adjuvants generally employed in,silver halide systems, the supports, and ,in the. relative. concentrations of the various components. 1

Various auxiliary layers may be present, such as antiabrasion over-coatings, subbing layers, and antihalation undercoats or backing layers. The elements may include multilayer well as monolayer structures. The various layers, including the support, may include inert ingredients, e.g., pigments, organic polymer latices, e.g., polyethyl acrylate or a butadiene/acrylonitrile copolymer, and matting agents, e.g., silica particles, starch etc. As disclosed in U.S. 3,155,507, the silver halide may be insolubilized by treatment with an appropriate organic compound either during emulsion manufacture or by treatment of the' coated element with a solution of the organic compound. 1

The dissolution developer (i.e., the solution of silver E halide solvent) may contain various adjuvants such as shown below in Example III. The only essential components for this invention, however, are water, a ilver halide solvent, and a Dmax maintainer. Numerous useful 4 silver halide solvents arealisclosed in U.S. 3,155,507 but in the present application only the use of preferred silver halide solvents which contain the thiosulfate anion will be described.

The Dmax maintainers of this invention are also useful in improving the images obtained according to the process of Haugh, U.S. Ser. No. 546,202 filed Apr. 29, 1966. This process gives unusual images in black and white or color for information analysis, masking, artistic efiee'ts, etc. 7 V

The invention will'be further illustrated by but is not intended to be limited to the following examples.

EXAMELE I A light-sensitive gelatino-silver chloride coagulum, made by precipitation and coagulation washing in the manner taught in Moede, U.S. Patent 2,772,165, was redispersed in an aqueous gelatin solution so as to achieve a gelatin to silver chloride 'weight ratio of 0.79. The resulting emulsion was digested at 170 F., for 20 minutes in the presence of 0.80 g. of 2-mercapto-4-phenylthiazole, and 0.025 g. of the merocyanine dye of Example I, U.S. 2,342,546, Feb. 22, 1944, per mole AgCl. Emulsion adjuvants were added, including gelatin hardening agents and coating 'aids, and the emulsion was coated on a vinyiidene chloride copolymer subbed polyester base prepared as described in Example IV of Alles, U.S. Patent 2,779,684 (and to which a gelatin sub-layer had been subsequently applied). The coating Weight was 46 mg./dm calculated as metallic silver.

A sample of the dried photosoluble film was exposed through a /2 stepwedge for 2 seconds at 20 inches distance from a high intensity, tungsten filament, incandescent lamp (General Electric Reflector Photoflood lamp, No. PH/RFL 2). The exposed film, serving as a control, was processed for 3 minutes at 68 F. in the following silver halide solvent solution:

Sodium thiosulfate, anhyd. g 57.5 Sodium sulfite, anliyd. L g 4.5

Solution of In distilled water, specific gravity 1.013 ml 20 H O to. .1 liter. Sodium hydroxide to pH of 11.0.

i Concentration grams/liter D maintainer D maintainer D Control None 0. 05 1-(1-naphthyD-2-thiourea 0. 024 2. 40 D0 .Z 0. 048 2. 86 0. 072 3. 35 0. 4+ 0. 24 2. l3 0. 36 3. 71 0. 48 4+ 0. 046 2. 24 0. 18 4+ The D -maintaining compounds were added from two or three percent solutions in Z-butoxyethanol, a solvent which has relatively little elfect on D at the high pH employed here.

Positive AgCl' images were obtained in all of the films 1 treated 'with the D maintainer compounds. All of the films were washed one minute in' tap water and given an overall exposure to white light from a suitable lamp. Then the images were intensified by treatment for 1 minute in a photographic silver halide developer of the following composition, which had been diluted 1:1 with water be fore use:

The films were then washed in water for 1 minute and dried in air, The intensified metallic silver images had maximum transmission optical density as recorded in the above table. Where the D is shown as 4+, the density was greater than could be detected by the densitometer.

EXAMPLE 11 Example I was essentially repeated except that the silver halide solvent solution was reduced in pH to 7.0 by the addition of acetic acid and various D -maintaining compounds were added to this solution as indicated in the table. The D -maintaining compounds were added from Z-butoxy-ethanol solutions, using a 2% by weight solution with 1-(1-naphthyl)-2-thiourea and using 3% by weight solutions of the other compounds. The one compound, 1-methyl-3-t-butyl-2-thiourea, was added from a 2.4% by weight solution in ethanol. Since the organic solvents themselves have a small effect as D maintainers, each substituted thiourea compound was tested with its own individual control wherein pure solvent was added to the silver halide solvent solution in the same quantity as was used as a vehicle for the substituted thiourea D -maintainer compound Example II was essentially repeated except for using a lower pH silver halide solvent solution of the following formulation:

Sodium thiosulfate, anhyd 77.0 g.

Sodium sulfite, anhyd 7.5 g. Borax 9.0 g. Potassium acetate 10.0 g.

CaHuQ (OCH2CH2)nSOsN a (n=5 or less) in distilled water, specific gravity 1.013. 20 ml. D -maintainer compound as indicated. Water to 1 liter. Acetic acid to pH of 5.0.

As in Example II the 1-methyl-3-t-butyl-2-thiourea was added from a 3% ethanol solution. The l-(l-naphthyD-Z- thiourea was added from a 2% solution of 2-butoxyethanol while the other D -maintainer compounds were added from a 3% solution of Z-butoxyethanol. Experimental results are given in the table below.

D m ll! Cone. Dm With Dim.

maintainer maintainer Dmnx, maintainer (g./l.) Control present Control 0 3. 44 l-(l-naphthyDZ-thiourea-- 0.048 3. 82 4+ 1-phenyl-2-thiourea 0.072 3. 82 4+ 1-methyl-3-t-butyl'z-thioure 0. 072 3. 28 4+ 1-ally-2-thiourea 0. 036 3. 40 4+ 6 EXAMPLE 1v Samples of the film described in Example I were soaked for 15 seconds at room temperature in solutions of various D -maintainer compounds of the following general formulation:

I Ml. Water 24 Polyethylene oxide surfactant solution of Example I 1 Acetone solution containing 1 g. D maintainer per A control strip of photosoluble film was soaked in a similar solution from which the D maintainer was omitted.

After drying, the film samples were exposed as in Example I and then treated for 3 minutes at 68 F. in the following silver halide solvent solution:

The strips were then washed, flashed to white light, intensified by treatment in a silver halide photographic developer solution, and given a final wash and drying, all as described in Example I. The results given below demonstrated the improvement efiected by the use of the substituted thiourea compounds:

D -maintainer D Control 2.64 1-(1-naphthyl)-2-thiourea 4+ 1,1-diphenyl-2-thiourea 4+ 1-phenyl-2-thiourea 4+ EXAMPLE V A photosoluble film was prepared by coating on the film base of Example I an aqueous gelatin dispersion of a spectrally sensitized silver chloride emulsion which contained 1.18 grams of the insolubilizer, benzoxazolethiol, per mole of silver chloride.

Another photosoluble element was prepared by coating a similar dispersion which contained 1.5 grams of the insolubilizer, p-bromothiophenol, er mole of silver chloride.

Four silver halide solvents were prepared which contained 10 grams of sodium sulfite, 32 grams of sodium thiosulfate, 5 ml. of the polyethylene oxide surfactant solution of Example I, a 2-butoxyethano1 solution of a D -maintainer as noted in the table below, and sulficient water to bring the volume up to 1 liter. The pH of each solution was adjusted with sodium hydroxide to 9.0.

mnx. Concentration, maintainer grams per liter Silver halide solvent:

A. Control 0 B l-(l-naphthyD-thionrea 0. 0024' C 1,1-diphenyl-thiourea 0. 0036 D l-phenyl-thiourea 0. 0036 7 maximum density is demonstrated by the data of the following table:

Silver halide solvent solution Photosoluble film insolubilized with:

11% (control) EXAMPLE VI A non-spectrally sensitized, large grain silver bromide photosoluble emulsion containing 0.63 grams of the insolubilizer, 2-mercapto-4-phenylthiazole, per mole of silver bromide was coated on the film base of Example I to yield a photosoluble film having a coating weight of 56.8 mg./dm. of silver bromide. Two film samples were exposed as in Example I. One of the samples was treated for 3 minutes in silver halide solvent solution A (control) while the other sample was treated for 3 minutes in silver halide solvent solution B of Example V. Both samples were then washed, intensified in a silver halide photographic developer solution, washed, and dried in air as described in Example I. The control film had a D of 0.4 while the film treated in the silver halide solvent solution B, containing 1-( l-naphthyl) thiourea, had a D 1.12.

EXAMPLE VII A spectrally sensitized photosoluble film was made from a lithographic silver bromochloride (30 mole percent AgBr, 70 mole percent AgCl) emulsion containing 0.67 g. of the insolubilizer, 1-phenyl-5-mercaptotetrazole, per mole of silver halide. The emulsion was coated on the film support of Example I. Two samples of the coated film were treated as were the two samples described in Example VI. The film treated in the control silver halide solvent solution had a D of 0.6 while the sample treated in silver halide solvent B, containing l-(l-naphthyl)-2-thiourea, had a D of 1.9.

EXAMPLE VIII A control silver halide solution A was prepared as follows:

(NH4)S203 g Polyethylene oxide surfactant solution of Example I ml 2-butoxyethanol ml 10 H O to 1 liter. pH adjusted with NaOH to 9.0.

Silver halide solvent solution B was prepared similarly except that the 2-butoxyethanol was replaced with 10 ml. of a 3% by weight solution of l-phenyl-Z-thiourea dissolved in 2-butoxyethanol.

Example I was repeated except for replacement of the silver halide solvent solutions of that example with solutions A and B of this example, treating the exposed film of Example I in these solutions for 3 minutes at 68 F. After intensification of the images as in Example I, the maximum density of the film treated in solution A (the control) was only 0.04 as compared with 3.3 for the film treated with the solution containing 1-phenyl-2-thiourea.

EXAMPLE IX A control silver halide solvent solution A was prepared by dissolving, in one liter of water, 57.5 g. of anhydrous sodium thiosulfate and 4.5 g. of anhydrous sodium sulfite. The solution was adjusted to pH 7.8 by addition of dilute acid. Silver halide solvent solution B was identical except for the addition of 1 g. per liter of the solid compound, 1-( l-naphthyl -2-thiourea.

Six exposed film strips as described in Example I were treated for one, two, or three minutes at 68 F. in the silver halide solvent solutions A and B as indicated in the table below. The strips were subsequently washed, flashed to white light, intensified washed and dried, all as described in Example I.

Treatment Silver halide time, solvent solution minute Dmnx.

The present invention has the advantages of the basic process of photosolubilization that are described in the patents listed above, especially that of a very simple, single step process of obtaining a positive image. Advantages over the basic process include increased optical densities in unexposed areas, both for silver halide images and for intensified images. Also, processing is simpler because the D maintainers make the elTects of such variables as concentration of silver halide solvent, solution pH, and processing times less critical. In particular, these substituted thiourea compounds permit processing at higher pH values than would be practical in their absence. Still other advantages will be apparent from the above description of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A process for forming a direct-positive silver halide image which comprises (a) exposing, imagewise, a photosoluble layer containing silver halide made relatively less soluble in a silver halide solvent by treatment with an organic compound containing sulfur and/or nitrogen and capable of forming a silver salt of lower solubility in water than silver chloride; and

(b) dissolving the exposed silver halide in a silver halide solvent comprising an aqueous bath of an alkali metalv or ammonium thiosulfate, the improvement being characterterized by the presence in said bath at pH from 3 to 11 of 0.01-2.08 per liter of a substituted thiourea compound free from ionizable iodine, or oxidizing or reducing groups which are active at the Working pH, in sufiicient quantity to retard solution of the unexposed silver halide.

2. A process according to claim 1 wherein said thiourea compound is l-(l-naphthyl)-2-thiourea.

3. A process according to claim 1 wherein said thiourea compound is l-phenyl-Z-thiourea.

4. A process according to claim 1 wherein said thiourea compound is 1,1-diphenyl-2-thiourea.

5. A photosoluble layer containing light-sensitive silver halide made less soluble in a silver halide solvent by treatment with an organic compound containing sulfur and/or nitrogen and capable of forming a silver salt of lower solubility in water than silver chloride, said layer containing in addition a different auxiliary organic compound and which is a substituted thiourea compound free from ionizable iodine, or oxidizing or reducing groups which are active at the working pH, in quantity of 0.0l2.08 per liter to further retard solution of unexposed silver halide of said layer.

6. A layer according to claim 5 wherein said organic compound is present in such an amount, in terms of the ratio of its weight to the surface area of the silver halide crystals, that when admixed in such ratio with an aqueous silver bromochloride, 30/70 mole percent, gelatin dispersion containing 0.29 mg. of Ag in one-half ml., and said silver bromochloride dispersion is treated with 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag and mg. of sodium thiosulfate, at least three times the amount of silver bromochloride remains undissolved as compared with a similar dispersion successively treated With 5% by Weight aqueous sodium hypochlorite and 10% by weight aqueous sodium thiosulfate, so that the resulting mixture contains 0.29 mg. of Ag. 25 mg. of sodium hypochlorite and 100 mg. of sodium thiosulfate, after vigorous agitation of both dispersions for 30 seconds at 25 C.

7. A layer according to claim 5 wherein said auxiliary compound is 1-(1-naphthyl)-2-thiourea.

8. A layer according to claim 5 wherein said auxiliary compound is 1-phenyl-2-thiourea.

10 9. A layer according to claim 5 wherein said auxiliary compound is 1,1-diphenyl-2-thiourea.

References Cited UNITED STATES PATENTS 3,155,507 11/1964 Blake 9664 NORMAN G. TORCHIN, Primary Examiner R. E. FICHTER, Assistant Examiner US. Cl. X.R. 9694 52 3 UNITED STATES PATENT dFFiCE CERTIFICATE OF CORRECTION Patent No. 3, 12? 9 Dated 7: 97

In'ventor(s) Ralph Kingsley Blake It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

F601. 8, claim 1, line .5, "0.01 2.08 per liter" should read --0.0l 2.0g. er liter same column, claim 5, line 65, "0.01 2.0 per liter" should read --0.01 2.0g. per liter--.

SIGNED AN'D SEALED JUL 1 41970 Atteat:

Edward M- Flemhm WILLIAM E. sum, JR. Attesting Officer Gomissioner of latents 

